1. Field of the Invention
The present invention relates to a color measuring device, an image forming apparatus, an image forming method, and a computer-readable storage medium.
2. Description of the Related Art
Image forming apparatuses, such as printers, perform a process called color management to prevent a variation in output due to device-specific characteristics in order to improve reproducibility of output with respect to input. The color management is performed by, for example, the following manner. First, an image forming apparatus actually outputs an image of a color chart (patch) in a reference color (hereinafter, the image of the patch output by the image forming apparatus is referred to as “a patch image”), and measures colors of the patch image by using a color measuring device. Then, a color conversion parameter is generated based on a difference between a colorimetric value of the patch image (measured color value) and a color value of a corresponding reference color in the standard color space, and the color conversion parameter is set in the image forming apparatus. Thereafter, when outputting an image of input image data, the image forming apparatus performs color conversion on the input image data based on the set color conversion parameter and outputs an image based on image data obtained by the color conversion. Therefore, the image forming apparatus can output images with high reproducibility while preventing a variation in output due to device-specific characteristics.
In the color management as described above, a spectrophotometer is widely used as a color measuring device for measuring colors of a patch image. The spectrophotometer can acquire spectral reflectance per wavelength, so that it can measure colors with high accuracy. However, the spectrophotometer includes a number of sensors and is therefore expensive. Therefore, there is a need to enable colorimetry to be performed with high accuracy by a device that is reasonable in price.
As one example of a method for realizing colorimetry at low costs, there is a method to capture an image of an object to be measured (color measurement target) by an image capturing device having an image sensor and convert an RGB value of the object obtained by image capturing into a color value in the standard color space. For example, Japanese Patent No. 3129502 discloses a technology, in which a reference color chart to be compared with an object is disposed near the object being the color measurement target, images of the object and the reference color chart are simultaneously captured by a color video camera, RGB data of the object is corrected by using RGB data of the color reference chart obtained by image capturing, and the RGB data of the object is converted into a color value in the standard color space.
However, in the technology disclosed in Japanese Patent No. 3129502, it is difficult to maintain a positional relation among the object, a light source, and the color video camera, so that an image capturing condition may vary every time an image is captured. Therefore, it is sometimes impossible to measure colors with high accuracy.
Therefore, there is a need to provide a color measuring device, an image forming apparatus, an image forming method, and a computer-readable storage medium capable of measuring colors with high accuracy.